docs: def pip(filename):
      """Parse pip reqs file and transform it to setuptools requirements."""
      requirements = []
      for line in open(join(ROOT, 'requirements', filename)):
          line = line.strip()
          if not line or '://' in line:
              continue
          match = RE_REQUIREMENT.match(line)
          if match:
              requirements.extend(pip(match.group('filename')))
          else:
              requirements.append(line)
      return requirements